Wastepaper containing pressure sensitive labels and tapes are generally considered nonrepulpable in paper recycling operations due to the presence of the adhesive. These adhesives are commonly used in label and tape products and are generally composed of acrylic and rubber (block copolymer) based polymers. These adhesives will firmly adhere to the fiber matrix of paper and are neither water soluble nor water dispersible which complicates their effective removal during the paper recycling operation.
During recycling processes, conventional adhesives tend to agglomerate and form globules, called "stickies." These stickies are contaminants which interfere with the paper pulping and de-inking operations and can deposit on the felts, wires, and drier cans of paper machines, thereby causing functional and cosmetic flaws in the resulting paper. Thus, waste paper containing conventional adhesives are generally not considered repulpable. They are usually landfilled. With the possibility of legislative mandates requiring the use of repulpable adhesives, banning paper from landfills, and an increasingly demanding environmentally sensitive public, introduction of repulpable adhesives to the marketplace would be highly beneficial.
In order to render adhesives repulpable in paper mills, several approaches have been exploited. One approach has been to use water dispersible adhesive technology. For example, U.S. Pat. Nos. 4,482,675, 4,569,960 and 5,196,504 disclose water dispersible adhesives made of acrylic copolymers. However, these polymers tend to have insufficient adhesive characteristics for many applications, as measured in low values in looptack and peel testing.
Another approach to the development of repulpable adhesives has been to use water soluble adhesive technology. For example U.S. Pat. Nos. 4,413,082 and 4,442,258, disclose water soluble adhesives made of butyl acrylic (BA)/acrylate acid (AA) based polymers. However, these adhesives suffer from poor shelf life, poor humidity and/or heat-aged performance, and a propensity to bleed into the paper facestock over time. Further, water soluble adhesives create a secondary problem in paper recycling operations. Thus, it is difficult to remove dissolved polymer from treated water, causing environmental problems when water is discharged from the mill.